Apparatus base configuration for reduction of sliding and tipping



Aug. 19, 1969 R. R.- STOKES 3 62,

APPARATUS BASE CONFIGURATION FOR REDUCTION OF SLIDING AND TIPPING FiledDec. 13, 1967 FIG. 3

FIG 4 //Vl ENTOR R. R. STOKES I ATTORNEY.

United States Patent O" US. Cl. 248-346 2 Claims ABSTRACT OF THEDISCLOSURE To reduce the tendency of apparatus to slide or tip inresponse to an applied force, two materials with diverse coefiicients offriction are selectively affixed to the base of the apparatus. Amaterial with a high coefficient of friction is afiixed to a portion ofthe apparatus base area and contacts the desk or utility surface uponwhich the apparatus is placed. A second material which is affixed to theuncovered perimeter of the base, and has a relatively low coefficient offriction, is offset so that it only comes into contact with the utilitysurface upon incipient tippin of the apparatus, thereby preventingfurther tipping by allowing the apparatus to slide.

BACKGROUND OF THE INVENTION Field of the invention This inventionpertains to equipment support apparatus and, more particularly, to baseapparatus for supporting diverse equipments subject to sliding andtipping.

Description of the prior art Desk or table top apparatus such astelephones, pen sets, ashtrays, etc., and other similar objects areoccasionally subject to abusive treatment. The most common and,potentially, the most damaging type of abuse results from inadvertentstriking, pushing or pulling of the apparatus in such a manner that theinstrument or other device is propelled across the top of a table ordesk on to the floor. To prevent this occurrence, devices, of the ortdiscussed, are generally supplied with base pads, afiixed to the bottomof the instrument, which effectively reduce this predilection to slide.The underlying mechanism of this relatively simple preventive techniqueis based upon the principle that the resistive or frictional forceexerted by a surface is directly related to the product of the reactiveforce of the surface, generally equal to the Weight of the apparatus,and the coefficient of friction of the base pad afiixed to the bottom ofthe device. Since the instrument will remain immobile when the appliedforce is less than the resistive frictional force, and will beaccelerated only by a force equal to the difference between the appliedand resistive forces, when the former exceeds the latter, it isdesirable to make the resistive force as large as possible, consonantwith the requirement that the surface upon which the apparatus rests notbe damaged. Since the weight of the instrument is generally invariant,the desired effect is achieved by using a base pad with a relativelyhigh coefiicient of friction.

The taller the device becomes, the more susceptible it is to a secondabusive action, namely, tipping. Tipping may be defined as the tendencyof an instrument to rotate about one edge of its base and fall on itsside in response to an applied striking force. Thus, for tipping tooccur, the edge of the base must remain stationary. To prevent tipping,it is therefore desirable that the edge slide rather than remainimmobile.

3,462,111 Patented Aug. 19, 1969 ice It is, of course, apparent that thecoefficients of friction required for the two conditions necessary toprevent sliding and tipping are mutually exclusive, i.e., thecoefficient of friction should be high to prevent sliding and low toprevent tipping.

It is, therefore, an object of this invention to reconcile theseconflicting criteria in a base pad configuration which simultaneouslyprevents sliding and tipping.

SUMMARY OF THE INVENTION This object is accomplished, in accordance withthe inventive principles described herein, by utilizing, simultaneously,two materials with diverse coefiicients of friction which areselectively affixed to the base of an apparatus. More particularly, inone embodiment of the invention, a material with a high coefiicient offriction is affixed to the central portion of an instrument base areaand contacts the desk or utility surface upon which the instrument isplaced. This centrally located material prevents sliding when a force isapplied to the instrument. A second material which occupies theuncovered perimeter of the base, and has a relatively low coefiicient offriction, is offset so that it only comes into contact with the utilitysurface upon incipient tipping of the instrument. Because of the lowcoefiicient of friction of the perimeter material, the instrument slidesrather than tips. As the instrument slows down, it rocks back into itsoriginal vertical position, bringing into play the increased frictionaleffect of the centrally located material. Thus, since there is a greaterchance of breakage if the apparatu tips over, moderate sliding isinduced, in accordance with this invention.

These and further features and objects of this invention, its nature andvarious advantages will be readily apprehended upon consideration of theattached drawings and of the following detailed description of thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a diagram of an illustrative instrument which is subject tosliding and tipping in response to applied forces;

FIG. 2 is a free body diagram which illustrates the mechanics of slidingand tipping;

FIG. 3 is an illustrative diagram of a base configuration, in accordancewith this invention, which substantially reduces sliding and tipping ofan attached instrument;

FIG. 4 is another view of the base configuration of FIG. 3;

FIG. 5 is an illustrative diagram of another embodiment of the baseconfiguration of this invention; and

FIG. 6 illustrates yet another embodiment of this invention.

DETAILED DESCRIPTION In the drawing of FIG. 1, there is illustrated aninstrument, for example, a television transceiver 11, having a base 12which rests on surface 13. (It should be noted, at the outset, that theprinciples of this invention are applicable to diverse and sundryapparatus including television receivers, lamps, racks, cabinets,telephones, pen sets, ashtrays and other miscellaneous desk top or floormounted apparatus.) The center of gravity of device 11 is indicated bythe designation c.g. Considering, first, force F which is applied at apoint below the center of gravity of the instrument, one intuitivelyfeels that if the force F exceeds the frictional resistive force of theutility surface 13, instrument 11 will slide rather than tip. On theother hand, considering force F which is applied to instrument 11 at apoint well above the center of gravity, intuition leads one to feel thatdevice 11 will tip rather than slide if the frictional force exerted onthe edge of base 12, by the utility surface 13, exceeds the magnitude offorce F Turning now to FIG. 2, which is a free body diagram of a device14 having arbitrarily selected contour dimensions, the frictional forceexerted by utility surface 13 is directly related to the product of thereactive force R and the effective coefficient of friction, of thecontact surface of base 15 of device 14. Force R, in the case where norotation has occurred, is equal to the weight (mg) of device 14. Thusthe frictional force may be expressed as:

frcsisting=l 1 l-1( g) Since device 14 will not slide when the appliedforce, F, is less than the force, fresisting, and will be acceleratedonly by the difference between these two forces, when the applied forceexceeds the resisting force, it is desirable to make the resisting forceas large as possible commensurate with not damaging the surface 13 uponwhich the device rests. This desired effect is generally achieved byaffixing to the contact surface of base 15 a material or .pad with ahigh effective coefficient of friction, [.01.

Having considered the mechanics of sliding, we turn now to theprinciples underlying the phenomenon of tipping. Assuming the appliedforce F is above the center of gravity and has rotated apparatus 14through an angle 7', then by taking moments about a point of coincidenceof the edge of base 15 and utility surface 13, i.e., the point ofapplication of reactive force R, a state of equilibrium will exist when:

1', cos 1') Fzmg) 1'2 in (1+ where r is equal to the length of theradius vector to the center of gravity c.g., r is equal to the length ofthe radius vector to the point of application of force F, 0 is equal tothe initial angle defined by radius vector 1', and surface 13, and 'y isequal to the initial angle defined by radius vector r and surface 13, asillustrated. Taking moments about the point of application of force F,the reactive force R is defined by:

Thus, it is seen that the requirements for the coefficient of frictionof the base of device 14, for the two conditions necessary to preventsliding and tipping, are incompatible. That is, the frictionalcoefficient, should be as high as practical to prevent sliding and thefrictional coefficient, should be as low as practical to preventtipping. It should, of course, be apparent that although the abovediscussion Was premised upon the analysis of a free body diagram of arelatively simple configuration, the principles derived are true in allcases.

FIGS. 3 and 4 illustrate an embodiment of the invention wherein thesetwo incompatible requirements are reconciled in a base pad configurationwhich substantially reduces the tendency of an instrument or otherapparatus to slide or tip in response to applied forces. Structure 15,which represents the supporting base of any arbitrarily configuredapparatus, not shown, has affixed to its utility contact or supportingsurface, by ad hesive or any other well-known technique, two materialswith diverse coefficients of friction. Material 16, which may compriseany well-known frictional material, e.g., a cellulose, rubber or feltcomposition, is affixed to the central portion of the instrument basearea, as may be more clearly seen from the plan view of FIG. 4, andcontacts the desk, floor or utility surface .13 upon which the apparatusrests. Material 16 has a high effective coefficient of friction, [1.1,illustratively in the range of 0.8 to 1.0, sufficient to satisfy therequirement of Equation 1 for anticipated maximum applied forces. Thus,material 16 prevents sliding of the base when a force is applied to theapparatus mounted on base 15. A second material 17, affixed to theuncovered perimeter, represented by border dimension x, of base 15, hasa coefficient of friction, ,u which satisfies the requirement ofEquation 5. In addition, material 17 is offset from surface 13 apredetermined distance represented by dimension y. The reduction in areaof material 16, necessary to accommodate the perimeter material 17, isnot significant since resistance to sliding is not a function of area.Consequently, for conditions of sliding, the base functions in a normalmanner.

In the case of tipping, however, base 15 rotates about edge 18 untiledge 19 touches surface 13. Of course, the amount of rotation may becontrolled by the magnitude of the offset and border width dimensions yand x. Indeed, the angle of rotation 'r necessary for edge 19 to contactsurface 13 is defined by the arctangent of the ratio of y to x. Indetermining the maximum coefiicient of friction for material 17, it isnecessary to substitute into Equation 5 the maximum allowable value of1- determined by dimensions y and x. In one particular embodiment,having values for 0 and 'y of 59.8 and 56.8, respectively, it was foundthat an initial rotation of 9.4 was obtained with dimensions of 0.02inch and 0.12 inch for y and x, respectively, yielding a maximumcoefiicient of friction equal to 0.57. Since rotation is an inherentpart of tipping, the low coefficient of friction material 17 isautomatically brought into play. Thus, the instrument will commencesliding rather than tipping since the edge 19, which comes into contactwith the utility surface 13, will not remain immobile. As soon as theinstrument slows down sufficiently to rotate in the opposite direction,the high coefiicient material 16 comes back into contact with surface13, applying a braking action and bringing the instrument to rest. Ofcourse, material 17 may, in appropriate cases, not comprise a separateand distinct frictional material but may, if it satisfies the constraintrelationship of Equation 5, be the base utility contact surfacematerial, itself. It has been found that the chrome plated edge of thebase of an instrument which is 13.6 inches high and has a base dimensionof 10.5 inches, performed satisfactorily. Of course, materials such asTeflon, or other similar compositions, may be used, if so desired.

FIG. 5 illustrates another embodiment of this invention wherein aplurality of frictional elements 16 are afiixed to an instrument base 15contact surface. By locating the material elements near the perimeter ofthe base but displaced therefrom, and utilizing the base contact surfaceitself for the low coefficient of friction material 17, as discussedabove, a lower average tipping angle is achieved. For the case of acircular base, three equidistant elements have a decided advantage. Theadvantage of three-point mounting is that, on the average, the angle ofrotation, 1, required to bring into play the lower coefiicient offriction material is reduced. Since T is defined by the arctangent ofthe ratio of y, the offset dimension, to x, the border dimension, '7' isa maximum when x is a minimum. However, as shown in FIG. 5, theeffective dimension x is a function of the location of the appliedforce. If the striking force occurs at F opposite a frictional element16, the angle of rotation 1- is the arctangent of y/x But, if thestriking force occurs at F adjacent to a frictional element 16, theeffective dimension x is equal to x Since the offset dimension y is thesame in both cases, the angle of rotation is decreased. For an arbitrarypoint of application of the striking force F the base will revert to oneor the other of the above tipping modes but, on the average, the angleof rotation is reduced.

FIG. 6 illustrates another embodiment of this invention where theadvantages flowing from three-point mounting are obtained by using africtional element 16, approximately triangular in shape, which isaffixed to the base of an apparatus. In environments where thefrictional material may absorb airborne oils and greases, and becomeembedded with dirt, thereby reducing its effective coefficient offriction, the larger the area of the pad 16 the greater is theprotection against undesired changes in the coefiicient ,u

It is to be understood that the embodiments shown and described hereinare illustrative of the principles of the invention only and thatfurther modifications of this invention may be implemented by thoseskilled in the art without departing from the scope and spirit of theinvention. For example, the configuration or contour of the frictionalmaterial or materials aflixed to the base of an apparatus may take manydiverse forms including, for illustrative purposes only, rings, bars,disks, bands, et cetera.

What is claimed is:

1. Base apparatus comprising:

base means for supporting attached apparatus upon a utility surface, theedge of the utility contact surface of said base means having apredetermined coefficient of friction #2 which allows the edge of saidbase means to slide along said utility surface after a predeterminedangle of rotation of said apparatus in response to an applied force, and

a frictional material afiixed to the utility contact surface of saidbase means, displaced from the edge of said base means a predetermineddistance, having an effective coefficient of friction ,u which exceedsthe quotient of the maximum expected applied force to said apparatus andthe weight of said apparatus.

2. An instrument, including a supporting base which is resistant tosliding and tipping comprising:

a first material affixed to the supporting surface of said base,displaced from the edge of said base a predetermined distance, having aneffective coefiicient of friction m which is greater than the quotientf/ mg where f is the expected maximum applied force to said instrumentand mg is the weight of said instrument, and

a second material, having a thickness less than that of said firstmaterial, affixed to the supporting surface of said base between saidfirst material and the edge of said base having a coefficient offriction #2 which is less than the expression 11 cos (0+7) 2 sin (v-i- &[cos (0+ 1') 2 005 (7+ where r, is the length of the radius vectororiginating at a point of coincidence of the edge of said base and asupporting utility surface and terminating at the center of gravity ofsaid instrument, r is the length of the radius vector originating atsaid point of coincidence of the edge of said base and said utilitysurface and terminating at the point of application of an applied forceto said instrument, 0 is the angle defined by radius vector r and saidutility surface, 'y is the angle defined by radius vector 1' and saidutility surface, and 1 is a predetermined angle of rotation of saidinstrument in response to an applied force.

References Cited UNITED STATES PATENTS CHANCELLOR E. HARRIS, PrimaryExaminer J. PETO, Assistant Examiner US. Cl. X.R. 16-42

